Method for working or forming metals in the presence of aqueous lubricants based on methanesulfonic acid

ABSTRACT

A method for working or forming metals which consists in usings an aqueous lubricant containing as water-soluble extreme pressure additive, methanesulphonic acid or water-soluble methanesulphonic acid salt. The water-soluble methane sulphonic acid salt is an alkali or alkaline-earth, ammonium, alkanol amine or ethoxylated fatty amine salt. The inventive aqueous lubricants have good extreme pressure properties and good properties with respect to corrosion.

FIELD OF THE INVENTION

The present invention relates to the field of lubricants and moreparticularly to that of aqueous lubricants containing water-solubleextreme pressure additives, and which are used for working or formingmetals.

BACKGROUND

Metal working or forming operations require the use of a lubricant inorder to reduce the forces between the part to be worked and the tool,to remove the chips and fragments, to cool the part or the plate worked,and to control its surface texture. Oil-based lubricants haveconventionally been used. These are whole oils or emulsions to whichlubricity promoters, antiwear (AW) and/or extreme pressure (EP)additives may have been added. EP additives are generally compoundscontaining sulfur. At the high temperatures prevailing at the contactbetween the metal parts during metal working operations, the sulfurcompounds decompose. A layer of iron sulfide is formed on the surface ofthe parts, hindering the processes of welding and adhesion.

Whole oils have excellent lubricating properties, but when productionrates are high, the removal of the heat generated requires the use ofemulsions. However, the use of emulsions also tends to be limitedbecause, over time, they deteriorate and give off foul odors. This iswhy the use of aqueous fluids is steadily spreading. These are eithersynthetic fluids, which are aqueous solutions based on water-solubleadditives, or semisynthetic fluids which are oil-in-water microemulsionscontaining a large quantity of emulsifiers. However, while the aqueousfluids effectively remove the heat and display improved resistance tobacterial proliferation, they are often limited to metal workingoperations in which the friction and wear conditions are not too severe.This is because EP additives have been developed specifically for oils,so that very few of these additives are water-soluble and thereforesuitable for aqueous fluids.

While numerous oil-soluble EP additives are available, the number ofwater-soluble EP additives is much smaller. In Lub. Eng. 1977, 3(6),291-298, R. W. Mould et al. describe the EP properties of a number ofwater-soluble sulfur-bearing additives, such as sodium salts ofthiosalicylic, 2-mercaptopropionic, 2,2′-dithiodibenzoic,2,2′-dithiodipropionic and dithiodiglycolic acids. Similarly, the use ofwater-soluble salts of 3,3′-dithiodipropionic acid has been the subjectof U.S. Pat. No. 4,880,552 and JP 63 265 997. In U.S. Pat. No.4,606,833, dithiodiglycol is used in combination with a derivative ofpolyoxyalkylene glycol to improve the extreme pressure properties ofaqueous lubricants. The use of derivatives of aminosulfonic acids asadditives in aqueous lubricating systems has been the subject of patentapplication WO 8602941. More recently, in Japanese patent application JP10 110 181, the water-soluble salts of 3,3′-dithiodipropionic acid werecombined with alkyl thioacids in aqueous drawing and stampinglubricants.

However, these products are not sufficiently stable in water. Theypromote bacterial proliferation and liberate hydrogen sulfide, causingthe aqueous fluids to emit a strong odor. Their formulation thusrequires the use of a large quantity of bactericides, which isincompatible with the quantities usually permitted in aqueouslubricants. Furthermore, some of these extreme pressure additives areincompatible with most of the other additives routinely used insynthetic and semisynthetic formulations.

Recently, lubricant compositions containing salts of sulfamic acidamines with extreme pressure effect have been the subject of patentapplication WO 00/44848. However, sulfamic acid is highly corrosive.Moreover, its low solubility precludes the production of liquidconcentrates that are easy to use in the formulations. Furthermore, tolimit the environmental impact of the lubricant formulations used in thefield of metal working and forming, it is particularly important toemploy readily biodegradable additives.

SUMMARY OF THE INVENTION

It has now been found that the use of methanesulfonic acid (MSA) or ofsalts of methanesulfonic acid in aqueous metal-working formulations isparticularly advantageous.

DETAILED DESCRIPTION

MSA is stable in water and completely soluble in all proportions atambient temperature. MSA is non-corrosive; in aqueous solution, itliberates no H₂S. MSA is readily biodegradable (100% decomposition in 28days), which is environmentally friendly. MSA confers particularlyadvantageous extreme pressure properties on the lubricant formulations.

The subject of the present invention is therefore a method for workingor forming metals in the presence of an aqueous lubricant containing awater-soluble extreme pressure additive, characterized in that thisadditive is methanesulfonic acid (MSA) or a water-soluble salt of MSA.

The water-soluble MSA salts according to the invention are obtained byneutralizing MSA with a salifying agent. Salts of alkali oralkaline-earth metals are preferred as water-soluble MSA salts accordingto the invention, but use can also be made of the water-soluble saltsobtained from compounds satisfying the general formula:R¹NR²R³where the symbols R¹, R² and R³, identical or different, each representa hydrogen atom, an alkyl, alkenyl or alkylaryl radical with 1 to 22carbon atoms, or an oxyethylated radical of the form (CH₂—CH₂—O)_(n)H,where n is between 1 and 20.

Among the alkali metal salts, those obtained by neutralizing MSA withcaustic soda or caustic potash are preferred.

As non-limiting examples of R¹NR²R³ compounds, mention may be made ofalkanolamines, in particular monoethanolamine, diethanolamine ortriethanolamine, ethoxylated amines whereof the preferred compounds arethose in which R¹ is a radical with 12 to 22 carbon atoms, and R² and R³are oxyethyl radicals with 1 to 10 ethylene oxide groups.

The salifying agent is added in stoichiometric proportion with respectto the MSA, in excess with respect to the MSA, or in deficiency withrespect to the MSA, depending on the pH desired for the finalformulation. Preferably, the molar ratio between the MSA and thesalifying agent is between 1:1 and 1:2.

The water-soluble MSA salts according to the invention are perfectlystable in water at ambient temperature and can be used to obtainconcentrated or dilute aqueous lubricant formulations which are easilystored without liberating any H₂S and have particularly advantageousextreme pressure properties.

Furthermore, these formulations are not corrosive.

The MSA or water-soluble MSA salts can be in the form of a concentratethat can subsequently be diluted during use, or in the form of a dilutesolution. They can be used alone, but in general they are used in amixture with other common additives of synthetic or semisynthetic fluidsfor metal working or forming. These additives include bactericides,emulsifiers, lubricity promoters, antiwear additives, antifoams andcorrosion inhibitors.

The concentrates contain between 10% and 50% by weight of MSA or ofwater-soluble MSA salt, and preferably between 15% and 35%.

The MSA or the water-soluble MSA salts according to the invention, theconcentrates containing same, and other additives conventionally foundin aqueous lubricants for metal working or forming, can be incorporatedwith the aqueous lubricants commonly employed for metal working orforming, and particularly with the synthetic fluids (true solutions) orsemisynthetic fluids (microemulsions), in concentrations between 0.01%and 20% by weight, and preferably between 0.1% and 10% by weight.

The efficiency of the extreme pressure additives according to theinvention is evaluated by tests on a 4-ball machine by the 4-ballextreme pressure test according to ASTM Standard D-2783: this testconsists in evaluating the extreme pressure capacity of a fluid from thevalue of the load above which 4 balls are welded together, preventingthe rotation of the uppermost ball on the other 3 remaining in the testfluid, according to the following measurement protocol:

-   -   100C6 steel balls 12.7 mm in diameter    -   Speed of rotation of the uppermost ball: 1500 revolutions per        minute    -   Test duration: 10 seconds    -   Increasing loads.

The load corresponding to the welding of the 4 balls corresponds to theextreme pressure capacity; it must be as high as possible, typically=160kg.

The anticorrosion power of the extreme pressure additives according tothe invention is evaluated by contacting chips of cast iron with theaqueous lubricant to be tested by the following protocol:

-   -   2 g of standard cast iron chips (ASTM D4627) are covered with 5        ml of aqueous lubricant to be tested in a petri dish with a        filter paper on the bottom.    -   Contact time: 2 hours at ambient temperature.

The appearance of rust on the filter paper is the indicator of theanticorrosion power; the grading is shown in Table 1:

TABLE 1 Observation on the filter paper Anticorrosion power No trace ofrust Good Few traces of rust Medium Traces of rust PoorThe following examples illustrate the invention without limiting it. Thepercentages indicated are expressed by weight.

EXAMPLES Example 1

Table 2 shows the composition and extreme pressure performance of thedifferent formulations tested; these are dilute aqueous formulations ofMSA or 1:1 water-soluble MSA salts. They contain 5% by weight ofwater-soluble additive.

These formulations are obtained at ambient temperature in a 300 mlbeaker containing 200 ml of double-distilled water. The adequatequantity of pure MSA is slowly added with moderate magnetic stirring.The caustic soda (NaOH), caustic potash (KOH), monoethanolamine (MEA),triethanolamine (TEA) or ethoxylated fatty amine (NORAMOX® C2: monoamineon ethoxylated copra base with 2 moles of ethylene oxide or NORAMOX® O2:monoamine on ethoxylated oleic base with 2 moles of ethylene oxide,manufactured by CECA) is then added in stoichiometric proportions toobtain a 1:1 salt containing 5% by weight of active material. Thesolutions are all clear, stable and without any particular odor. Each ofthe compositions was subjected to the 4-ball test with determination ofthe welding load.

TABLE 2 Composition Welding load Formulation Water (in %) Additive (in%) (in kg) Control 100 None 80 1 95 MSA 5 400 2 95 MSA 3.53 400 NaOH1.47 3 95 MSA 3.16 400 KOH 1.84 4 95 MSA 3.06 250 MEA 1.94 5 95 MSA 1.96200 TEA 3.04 6 95 MSA 1.19 160 Noramox C2 3.81 7 95 MSA 1.04 160 NoramoxO2 3.96

An examination of the results of the 4-ball test reveals that thelubricant formulations based on MSA or a water-soluble MSA saltaccording to the invention help to obtain a welding load=160 kg, muchhigher than the load measured with pure water used as a control. Theincorporation of an additive based on MSA or a water-soluble MSA saltaccording to the invention helps to provide extreme pressure propertiesto the aqueous formulations used for metal working or forming. The MSAand Na and K salts of MSA help to obtain the highest efficiency.

Example 2

Table 3 shows the extreme pressure performance and corrosion propertiesof two aqueous lubricants containing a water-soluble MSA salt accordingto the invention. These compositions are prepared by neutralizing MSAwith an excess of caustic soda (NaOH) or monoethanolamine (MEA). Thewater-soluble salt is in a concentration of 5% by weight in water; thecompositions are clear, stable and without any particular odor.

TABLE 3 Weld- Anti- Formul- AMS NaOH MEA ing load corro- ation (inmoles) (in moles) (in moles) (in kg) sion grade 8 1 1.25 — 500 Good 9 1— 2 200 Good

Compositions 8 and 9 according to the invention help to obtain highwelding loads in the 4-ball EP test. They have good corrosionproperties.

1. A method for working or forming metals in the presence of an aqueouslubricant wherein the improvement comprises adding a water-solubleextreme pressure additive comprising from about 0.01 to about 20 percentby weight a water-soluble salt of methanesulfonic acid comprising a saltof an alkali or alkaline-earth metal, or of a compound of the formula:R¹NR²R³ wherein R¹, R² and R³, are identical or different, each ahydrogen atom, an alkyl, alkenyl or alkylaryl radical with 1 to 22carbon atoms, or an oxyethylated radical of the form (CH2-CHrO)nH, wheren is between 1 and 20 to said aqueous lubricant.
 2. The method asclaimed in claim 1, wherein said water soluble methanesulfonic acid saltis a sodium or potassium salt.
 3. The method as claimed in claim 1,wherein said compound of the formula R¹NR²R³ is an alkanolamine.
 4. Themethod of claim 3 wherein said alkanolamine is a monoethanolamine,diethanolamine or triethanolamine.
 5. The method as claimed in claim 1,wherein said compound of the formula R¹NR²R³ is an ethoxylated amine inwhich R¹ is a radical with 12 to 22 carbon atoms and R² and R³ areoxyethylated radicals of the formula (CH₂—CH₂—O)nH with n between 1 and10.
 6. The method of claimed in claim 1 wherein the concentration ofwater-soluble methanesulfonic acid salt in said aqueous lubricant isbetween about 0.1% and 10% by weight.